using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Thing unique1 = new Thing("test", 1);

        Thing unique2 = new Thing("test1", 1);

        Thing unique3 = new Thing("test", 2);

        Thing dup1 = new Thing("test", 1);

        Thing dup2 = new Thing("test", 1);

        Thing[] things = {

            unique1,

            unique2,

            unique3,

            dup1,

            dup2

        };

        List<Thing> duplicateThings = 

            things

                .GroupBy(thing => new { thing.Name, thing.ServiceGroup })

                .Where(group => group.Count() > 1)

                .SelectMany(group => group.ToList())

                .ToList();

        foreach(Thing thing in duplicateThings)

        {

            Console.WriteLine("{0}:{1}", thing.Name, thing.ServiceGroup);

        }

    }

    public class Thing

    {

        public string Name { get; set; }

        public int ServiceGroup { get; set; }

        public Thing(string name, int serviceGroup)

        {

            this.Name = name;

            this.ServiceGroup = serviceGroup;

        }

        public Thing()

        {

        }

    }

}